Piezoelectric transducers are used in many technologies, including mechanical actuators or sonic and ultrasonic sources by applying an excitation voltage to their electrodes, or as sensors of stress or vibratory motions by detecting the voltage generated by the transducer when it is subjected to a mechanical force. Basically, the piezoelectric effect is an interrelationship between mechanical distortion and electrical effects, peculiar to certain crystalline materials. The nature and magnitude of a piezoelectric effect in a substance are dependent on the direction of applied force or electric field with respect to the crystallographic axes of the substance, i.e., it polarization. This polarization is one of several factors that determine the motion of a piezoelectric transducer, with other factors being the shape of the transducer, the manner in which the transducer is energized, and the manner in which two or more piezoelectric elements may be assembled to form a composite transducer.
Piezoelectric transducers made from polarized ceramic materials are especially useful because of their high piezoelectric sensitivity and geometric formability. Existing piezoelectric ceramic transducers have a number of shapes, such as disks, plates, rods, and cylinders.
Composite piezoelectric transducers consist of two or more bars, plates, or cylinders, rigidly bonded together. One form of composite transducer is a planar assembly, in which one piezoelectric plate is bonded to either another piezoelectric plate or to a passive plate. These transducers may be polarized and energized to form longitudinal extender transducers or bender transducers. Bender transducers are referred to as such, because, when activated, their motion involves flexural bending of the composite assembly relative to the planar surface of the transducer when not activated. Another form of composite piezoelectric transducer is cylindrical in shape. These transducers have assemblies of adjacent sections or of an inner and outer cylinder. They may be polarized radially, i.e., through their thickness, or axially, i.e., along the length of the axis. When polarized, they may be energized to undergo uniform expansion and contraction or to undergo flexural motion of the cylinder walls. The latter transducers are referred to as bender transducers.
Composite cylindrical transducers are the subject of U.S. Pat. No. 4,525,645, entitled "Cylindrical Bender-pending Type Vibration Transducer",issued Jun. 25, 1985, and co-pending U.S. Pat. No. 07/406,797, entitled "Piezoelectric Cylindrical Transducer for Producing or Detecting Asymmetrical Vibrations", filed Sep. 13, 1989. U.S. Pat. No. 4,525,645 and U.S. Pat. No. 07/406,797 are both assigned to the same assignee as the present invention.
Although composite transducers are successful in application, their structure makes them relatively expensive to make. Also, they are subject to limitations imposed by parts tolerances, by physical properties of the bonding material used to form the composite, and by the need for means for attaching electrodes.
A need exists for a transducer that produces the flexural motion of a composite transducer, but is more easily manufactured.